PB2392: MRNA IDENTIFICATION OF TIGIT IN PERITUMORAL LYMPHOCYTES IN CLASSICAL HODGKIN DISEASE
Authors: Ombretta Annibali, Valeria Tomarchio, Martina Verri, Maria Antonietta Tafuri, Antonella Bianchi, Anna Crescenzi, Luigi Rigacci
Journal: HemaSphere (2023)

Topic: 20. Lymphoma Biology & Translational Research Background: Hodgkin lymphoma is a rare B-cell malignant neoplasm represents approximately 11% of all lymphomas and with current treatment about 90% of all patients will be long-term survivors. T cell Ig and ITIM domains (TIGIT) has been recognized as an immune checkpoint receptor able to negatively regulate T cell functions. TIGIT has been shown to play an important role in modulating immune responses in the context of autoimmunity and cancer. Recently, our group (Annibali O et al. Sci Rep. 2021) demonstrated the TIGIT expression in lymphocytes around the RS cells using immunohistochemistry in 56% of evaluated patients. (19/34) Aims: Aim of this new study was to assess the in situ TIGIT mRNA expression in CHL, in order to verify the effective intracellular transcription of TIGIT receptor in peritumoral lymphocytes that resulted positive at immunohistochemical analysis. Secondary endpoints were to quantify the in situ hybridation signal and to compare the quantitative analysis of mRNA expression with the immunohistochemical score proposed in the previous study Methods: Thirty-four formalin fixed-paraffin embedded samples, in which was tested TIGIT protein expression, were selected. The TIGIT protein expression status was determined by immunohistochemical investigations with TiGIT antibody, as previously described. Seriate sections from FFPE lymph nodes were submitted for RNAscope Assay. Results: Among 34 enrolled cases, 15 resulted negative for TIGIT immunohistochemistry on lymphocytes within the tumor environment and were classified score 0. Ten cases showed a sparse, faintly stained non-tumoral lymphocytes within the tumor environment, near the HRS cells and were classified as score 1. Five cases showed the presence of a discrete quote of non-tumoral lymphocytes with moderate membrane staining around the HRS cells and were reported as score 2. Four cases demonstrated evidence of a circle of non-tumoral lymphocytes with intense membrane staining, surrounding the HRS cells corresponding to the score 3. RNAscope was successfully applied to the whole FFPE histological sections of the 34 Hodgkin’s lymphoma cases. TIGIT probe is represented as red dots/spots within the lymphocytes surrounding the RS cell. After slides were visualized, each case was assigned a semi-quantitative score based on the mRNA expression level of the TIGIT gene according to the scoring system provided by the RNAscope manufacturer. Low mRNA expression was observed in ten cases marked as “1” which is equivalent to 1-3 probe signals per positive lymphocyte. Five cases showed moderate mRNA expression with a score of “2” representing 4-10 probe signals per positive lymphocyte. Four cases showed high mRNA expression with a score of “3,” representing > 11 probe signals per positive lymphocyte. The remaining cases scored a “0” with no mRNA probe signals observed in the lymphocytes. With QuPath software, we observed an increase in the number of positive cells in relation to protein expression status. In fact, at score 0 corresponds 0% positive cells, at score 1+ corresponds 8% positive cells, at score 2+ corresponds 33% positive cells and at score 3+ corresponds 54.9% positive cells. Summary/Conclusion: Our results confirm the presence of immunoescape through the expression of TIGIT in patients with Hodgkin’s lymphoma, based on the expression of the mRNA coding for TIGIT and validate the score system proposed for the immunohistochemical reaction using a counting system with supervised computer algorithm. These data provide the rationale for the exploration of new target therapy using Tigit antibodies in patients with relapsed/refractory cHL Keywords: Hodgkin’s lymphoma